1. Field of the Invention
The present invention relates to synchrotron radiation measurement technology which is suitably used in various types of apparatuses, such as spectroscopes, lithography apparatuses, X-ray microscopes, etc., using synchrotron radiation.
2. Description of the Related Art
Synchrotron radiation which is generated when charged particles which are accelerated to high speeds are deflected by a magnetic field may be obtained as a sheet-shaped beam which is concentrated in the plane of the trajectory of the charged particles. This beam has a nearly Gaussian intensity distribution with respect to a direction perpendicular to the plane of the trajectory of the charged particles. The divergence of this beam, that is, the thickness (the magnitude of the spread, the size in the thickness direction) of the sheet beam, depends on the acceleration energy of the charged particles, the intensity of the magnetic field, the size of the charged particle beam, the divergence angle of the charged particle beam, etc.
When measurement, processing, etc., is performed using synchrotron radiation, normally, a beam is deflected or concentrated using a mirror and is irradiated onto a specimen. The concentration position and the intensity of the beam irradiated onto the specimen depend on the position of the beam which enters a mirror, and the magnitude of the spread thereof. In order to determine the intensity and the position of the light to be irradiated onto the specimen and to adjust the radiation to an optimal value, it is necessary to measure the position and the size of the beam. Also, when the synchrotron light source is controlled so that the position of the beam and the magnitude of the spread thereof are maintained at predetermined values, it is necessary to measure the position of the beam and the magnitude of the spread thereof.
Conventionally, as a method for measuring a synchrotron radiation beam, a method using a detector such as that shown in FIG. 18 is known. This detector is located inside a vacuum container, and includes an aperture plate 35 in which a pin hole 34 is provided, a filter 16 located behind the aperture plate 35, and a photodiode 36, so that the position of a sheet-shaped beam 15 can be measured.
This detector is moved to scan in a Y direction with respect to the synchrotron beam so as to determine the beam profile. Fitting by an appropriate function, for example, a Gaussian function, is performed thereon in order to calculate the spread (magnitude) a of the beam and the position thereof in the Y direction. That is, as shown in FIG. 19, in the horizontal axis, the position Y of the X-ray detector is plotted, in the vertical direction, the output (light intensity) S of the X-ray detector is plotted, and the measured values are plotted. Then, in order that it coincide well with this measured value, σ of the Gaussian distribution and the center value thereof are determined by performing Gaussian fitting such as that indicated by the solid line. More specifically, parameters of σ of Gaussian and the center value are determined so that, for example, the sum of the squares of the differences between the assumed Gaussian and the measured values is minimized.
However, there are points to be improved, such as those described below. That is, according to this conventional example, in order to determine the position of the beam and the size thereof with high accuracy, it is necessary to set the Y position of the X-ray detector precisely at the time of measurement and to perform measurements repeatedly so as to obtain a substantial amount of data. The X-ray detector is driven in increments of, for example, 0.1 mm, and measurements are therefore performed at 101 points over 10 mm. At this time, since an operation for driving a very small distance for each measurement and then inputting the output of the X-ray detector must be repeatedly performed, the measurements take a long time. For example, even when the measurement of one point takes 0.1 second, 10 seconds or more is required for all the measurements. There may be cases where the position and the size of the synchrotron radiation beam vary over short periods, but such a conventional method cannot detect variations at such short periods.
Also, if the position and the size of the beam vary while the detector is made to scan to measure the beam profile, it is not possible to accurately measure the beam profile, causing errors to occur in the measured values of the position and the size of the beam.